1. Field of Invention
This invention relates generally to the hydraulic generation of rotational energy, particularly to the transmission of torque from fluid flow using a magnetic coupling to generate power.
2. Prior-Art
Flow Meters
Many types of machines for converting mechanical or hydraulic power to electric power are known. In U.S. Pat. No. 6,212,959 (2001) Perkins teaches a flow meter which comprises a turbine within a pipe and coils exterior to the pipe. The axis of the turbine is parallel to the axis of the pipe. At least one permanent magnet is affixed to the turbine. As water flows through the pipe, the turbine turns. As the turbine turns, the magnetic field lines from the moving permanent magnet(s) pass through the pipe wall, intersect a coil outside the pipe, and generate a current within the coil. This current passes through a load resistance and generates a voltage which is proportional to the rate of rotation of the turbine, which in turn is proportional to the flow of water through the pipe. This voltage is measured by a microprocessor circuit and converted to a reading indicative of the flow rate.
While this arrangement accurately measures flow, it is not designed to provide significant power output, e.g., as can be utilized by electric machinery, appliances, or light sources.
Hydroelectric Generators
Another well-known type of converter is the hydroelectric generator. They are seen on dams, for example. Water is stored on the upstream side of the dam at a considerable depth—200 meters is not uncommon. The water head at the base of the dam is equal to 4 the depth of the water stored. The pressure due to the head (difference in height from the surface of the water to the turbine) represents a significant potential energy stored in the water.
A turbine is located at the base of the dam on the downstream side. Water flows from the upstream side through large pipes called penstocks, through the turbine, and out on the downstream side, usually to a river or stream. As the water flows through the turbine, its head is converted to rotational kinetic energy. The shaft of the turbine turns an electrical generator in well-known fashion, thus converting the rotational kinetic energy to electric power.
The turbine and the generator are separate machines that are connected by a common shaft. The shaft passes from the fluid-filled region containing the turbine blades, through a water seal and out into the dry region containing the generator.
In the interest of efficiency, it is normal practice for the turbine to extract the maximum possible amount of energy from the flowing water. Thus the water head at the output of the turbine is at a minimum value. Varying the output of the generator is accomplished by adjusting the flow of water through the turbine. While this system generates a large amount of electricity, little water pressure is available for other uses after passage through the turbine. And while the electricity generated is available to an end user, the end user is unable to adjust the flow of water through the turbine in proportion to their needs. In addition, these generating systems are typically very large and immobile.
Magnetic Stirrers
Still another type of converter is found in chemistry, where some processes require controlled agitation within a sealed vessel. The ability of magnetism to penetrate the vessel has been used to impart rotation to a magnetic stirrer. This process involves the expenditure of energy for the purpose of doing work within the sealed environment, and is not intended to harvest energy for storage or transformation as an addition to the function of a fluid delivery system.
FIGS. 1 and 2—Turbine—Description
FIGS. 1 and 2 show a cross-sectional side view and an axial view, respectively, of a turbine 100 contained within a pipe 105. Turbine 100 is mounted on a shaft 110 which terminates in bearings 115. Four blades 112 are joined to shaft 110 at an acute angle with respect to the axis of shaft 110. All four blades are shown in full view in FIG. 2, while only three can be seen in FIG. 1 (one edge-on and two in full view). Fluid passing through turbine 100 impinges on blades 112, causing them to rotate. In this example, when a fluid flows in the direction of arrows 125, the blades rotate clockwise. Typically, although four blades are shown in FIGS. 1 and 2, there can be any number of blades depending upon the size and design of the turbine and pipe assembly, such as between two and several hundred blades. Turbine 100 can be made of steel, plastic, or another suitable material. The assembly comprising turbine 100, shaft 110, and bearings 115 is supported by struts 120 affixed to the interior of pipe 105. The outer diameter of turbine 100 is preferably equal to at least ninety-five percent of the inside diameter of pipe 105. This ensures that fluid flow, indicated by arrows 125, impinges primarily on angled blades 112, causing turbine 100 it to rotate. When a fluid, such as water, flows through pipe 105, turbine 100 turns at a rate proportional to the flow.
Operation
If turbine 100 is allowed to turn freely, pressure p1 in a flow Region 1 before turbine 100 is nominally equal to pressure p2 in a flow Region 2 after turbine 100. If, through some action as explained below, rotation of turbine 100 is impeded, then p1 will be greater than p2.
In FIG. 1, the same volume of fluid is contained within Regions 1 and 2. In this example, pipe 105 is of constant diameter, and the fluid indicated by flow arrows 125 is incompressible. In this case, the energy equation, well known to those skilled in the art of hydrodynamics, reduces to:
      H    =                            (                                    p                              ρ                ⁢                                                                  ⁢                g                                      +                                          V                2                                            2                ⁢                g                                      +            z                    )                2            -                        (                                    p                              ρ                ⁢                                                                  ⁢                g                                      +                                          V                2                                            2                ⁢                g                                      +            z                    )                1              ,where H is the head or pressure difference between input and output of the turbine, subscript 1 indicates those parameters in Region 1 before turbine 100, subscript 2 indicates those parameters in Region 2 after turbine 100, p is the pressure at each region, ρ is the density of the fluid (water in this example) g is the acceleration due to gravity, V is the average velocity of the fluid in each region, and z is the height in each region. Other factors which influence head, such as friction, temperature differences, and the like are ignored in the present discussion. The above equation indicates that the head is generally proportional to the difference in height, pressure, and velocity between Regions 1 and 2.